The ventilation of car parks is important to prevent the build-up of toxic fumes and flammable gases from motor exhausts, and to clear smoke in the event of a fire. The Building Regulations (in particular Approved Document B and Approved Document F) specify what is required to maintain safe conditions in a car park. Further guidance is also given in BS 7346-7:2013.
There are broadly two methods of complying with the Building Regulations regarding ventilation and these are natural or mechanical ventilation. Whichever method is used, the required results are defined as:
- Smoke clearance:
To provide sufficient openings for enclosed car parks to allow any smoke being produced to leave the space naturally, or if this cannot be achieved then to remove smoke via a mechanical extract system.
- Fume exhaust:
To provide sufficient openings arranged such that a through draught at low/mid level is created to allow CO to leave the car park naturally, or if this cannot be achieved then to limit the concentration of CO within the space via a mechanical extract system.
The simplest method of complying with the regulations is by using natural ventilation by providing openings to the outside to vent smoke and fumes. However, in covered car parks this is usually quite difficult and as a result mechanical ventilation systems are employed. The most commonly used system today utilises jet or impulse fans to drive fumes or smoke towards extract fans – which keeps pollution within acceptable levels and enables effective smoke clearance when required.
For most small to medium sized car parks the ventilation system will be designed to control pollution and clear smoke. The extract fans will be sized on an extract rate of 6 air changes for fume control and 10 air changes for smoke clearance. Jet fans are selected on a grid basis with the coverage of each fan determined by its characteristics.
A control system will be provided to automatically operate the fans according to the conditions in the space to save energy and will usually incorporate CO sensors and fans speed control.
The design and installation of such systems is well within the realm of competent mechanical and electrical contractors with advice on product selection from reputable manufacturers. Easivent has developed a range of standardised solutions for car park ventilation which can be installed by our Approved Installer Network. Alternatively, you can become an Approved Installer yourself and implement our range in your projects.
Using jet fans it is possible to provide a more sophisticated system than ‘smoke clearance’ which is intended to offer safe conditions for occupants escaping the car park in a fire, and to assist firefighters in locating and extinguishing the fire. Design of such systems should be undertaken by a fire engineering specialist.
Jet fan systems can be more economical than smoke clearance for large car parks and contribute to future energy savings in the building.